The present invention relates to an apparatus for introducing measured or dosed quantities of pulverized or pulverulent materials into a carrier gas stream.
An apparatus for proportioning and extracting pulverized materials of the type herein discussed, has been disclosed in European patent application No. 0108319 as well as in Luxembourg patent application No. 84-462 corresponding to U.S. patent application Ser. No. 550,565, and Luxembourg patent application No. 84-780 corresponding to U.S. patent application Ser. No. 604,465, the two U.S. patent applications being assigned to the assignee hereof, all the contents of which are incorporated herein by reference. The invention described in European patent application No. 0108319 and the pending U.S. applications are particularly applicable to the operation of injecting solid fuels into a shaft furnace during a metal refining process.
In the dosing apparatus described in the above-mentioned patent applications, rotation of the movable sleeve is permitted by integrally attaching a rotor thereto having an axial cylindrical extension engaging a corresponding axial boring in a rotary drive shaft. This drive shaft is mounted in the housing of the apparatus with the aid of ball bearings and is fixed in the axial direction. The rotor is non-rotatable relative to the drive shaft, e.g. made fast in rotation therewith by means of a key, but retains freedom of movement in the axial direction and is subject to the action of a spring in the direction opposite to the shaft.
While suitable for its intended purposes, this prior art dosing device suffers from certain drawbacks. For example, the rotor which is attached to the movable sleeve is kept in an overhanging position by the end of the shaft. In turn, the overhanging portion itself has an overhang as a result of the comparatively small distance separating the two ball bearings. Since a certain clearance also has to be left between the rotor and the box, in order to preclude seizing, and since the movable sleeve is subjected to pressure in the reservoir holding the pulverulent materials, this pressure exerts a moment on the rotor and the housing on the side opposite to that on which the admission of the pulverulent material takes place. This moment also tends to increase the clearance between the rotor and the drive shaft.
The keying between the rotor and the drive shaft is similarly subject to increases in play in the direction of rotation, resulting in a progressive worsening or decay in the degree of accuracy in the proportioning of the material.